For electromagnetic wave (EMW) absorption materials, combining microstructure design with macrostructure design is considered as an effective means to adjust EMW absorption performance. Undoubtedly, the great advantages of three-dimensional (3D) printing technology in structural design and accurate molding provide a convenient and feasible research scheme for the adjustment of EMW absorption performance. In this study, a method combined 3D printing technology with direct chemical vapor infiltration (CVI) has been adopted to fabricate Al2O3/SiC whisker (SiCw) honeycomb composites. The porous oblique honeycomb structures with well-designed angle (30 degrees, 45 degrees, 60 degrees and 75 degrees) and micron-scale SiCw effectively improved impedance match, inner scattering and dielectric loss, which resulted in the realization of the optimized wave absorbing composites. Specially, Al2O3/SiCw composite with the angle of 30 degrees shows a minimum reflection coefficient (RCmin) value of -63.65 dB (99.9999%) absorption at 9.8 GHz with a thickness of 3.5 mm while the effective absorption bandwidth (EAB) ranges from 8.2 to 12.4 GHz, covering the whole X band. Besides, the EMW absorption mechanism for 3D printed Al2O3/SiCw composite is also discussed. As a proof of concept, this strategy provides a novel and effective avenue to fabricate structural composites with broader and higher microwave absorption performance.